U.S. patent application number 12/604094 was filed with the patent office on 2010-04-29 for fabrication of high-throughput nano-imprint lithography templates.
This patent application is currently assigned to MOLECULAR IMPRINTS, INC.. Invention is credited to Edward B. Fletcher, Weijun Liu, Marlon Menezes, Kosta S. Selinidis, Fen Wan, Frank Y. Xu.
Application Number | 20100104852 12/604094 |
Document ID | / |
Family ID | 42117806 |
Filed Date | 2010-04-29 |
United States Patent
Application |
20100104852 |
Kind Code |
A1 |
Fletcher; Edward B. ; et
al. |
April 29, 2010 |
Fabrication of High-Throughput Nano-Imprint Lithography
Templates
Abstract
An imprint lithography template includes a porous material
defining a multiplicity of pores with an average pore size of at
least about 0.4 nm. The porous material includes silicon and
oxygen, and a ratio of Young's modulus (E) to relative density of
the porous material with respect to fused silica
(p.sub.porous/p.sub.fused silica) is at least about 10:1. A
refractive index of the porous material is between about 1.4 and
1.5. The porous material may form an intermediate layer or a cap
layer of an imprint lithography template. The template may include
a pore seal layer between a porous layer and a cap layer, or a pore
seal layer on top of a cap layer.
Inventors: |
Fletcher; Edward B.;
(Austin, TX) ; Xu; Frank Y.; (Round Rock, TX)
; Liu; Weijun; (Cedar Park, TX) ; Wan; Fen;
(Austin, TX) ; Menezes; Marlon; (Austin, TX)
; Selinidis; Kosta S.; (Austin, TX) |
Correspondence
Address: |
MOLECULAR IMPRINTS
PO BOX 81536
AUSTIN
TX
78708-1536
US
|
Assignee: |
MOLECULAR IMPRINTS, INC.
Austin
TX
|
Family ID: |
42117806 |
Appl. No.: |
12/604094 |
Filed: |
October 22, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61227395 |
Jul 21, 2009 |
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61107720 |
Oct 23, 2008 |
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61110051 |
Oct 31, 2008 |
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Current U.S.
Class: |
428/315.5 ;
216/52; 216/56; 427/248.1; 427/256; 427/402; 427/569; 428/338 |
Current CPC
Class: |
B82Y 40/00 20130101;
G03F 7/0002 20130101; Y10T 428/249978 20150401; G03F 7/0017
20130101; Y10T 428/268 20150115; B82Y 10/00 20130101 |
Class at
Publication: |
428/315.5 ;
428/338; 427/402; 216/56; 427/248.1; 216/52; 427/256; 427/569 |
International
Class: |
B32B 3/26 20060101
B32B003/26; B05D 3/10 20060101 B05D003/10; B01D 3/00 20060101
B01D003/00; C23C 16/00 20060101 C23C016/00; B05D 3/06 20060101
B05D003/06 |
Claims
1. A imprint lithography template comprising: a porous material
defining a multiplicity of pores with an average pore size of at
least about 0.4 nm, wherein the porous material comprises silicon
and oxygen, a refractive index of the porous material is between
about 1.4 and about 1.5, and a ratio of Young's modulus (E, GPa) to
relative density of the porous material with respect to fused
silica (p.sub.porous/p.sub.fused silica) is at least about
10:1.
2. The imprint lithography template of claim 1, wherein the Young's
modulus of the porous material is at least about 10 GPa.
3. The imprint lithography template of claim 1, wherein the
relative density of the porous material with respect to fused
silica is at least about 50%.
4. The imprint lithography template of claim 1, wherein the porous
material comprises SiO.sub.x, and 1.ltoreq..times..ltoreq.2.5.
5. The imprint lithography template of claim 1, wherein the pores
are interconnected.
6. The imprint lithography template of claim 1, wherein the
template further comprises a base layer and a cap layer, and the
porous material forms a layer between the base layer and the cap
layer.
7. The imprint lithography template of claim 6, wherein stress in
the porous material is neutral to compressive.
8. The imprint lithography template of claim 6, wherein the porous
material comprises a non-uniform porosity gradient.
9. The imprint lithography template of claim 6, further comprising
a seal layer adhered to the cap layer, wherein the seal layer is
permeable to helium gas in contact with the seal layer and
substantially impermeable to species larger than helium.
10. The imprint lithography template of claim 9, wherein the seal
layer is positioned between the porous layer and the cap layer.
11. The imprint lithography template of claim 9, wherein a
thickness of the seal layer is less than about 10 nm.
12. A method of forming an imprint lithography template, the method
comprising: forming a layer of porous material on a surface of an
imprint lithography template, the porous layer defining a
multiplicity of pores with an average pore size of at least about
0.4 nm, wherein: the porous material comprises oxygen and silicon,
a refractive index of the porous material is between about 1.4 and
about 1.5, and a ratio of Young's modulus (E, GPa) to relative
density of the porous material with respect to fused silica
(p.sub.porous/p.sub.fused silica) is at least about 10:1.
13. The method of claim 12, further comprising forming a second
layer on the porous layer.
14. The method of claim 12, further comprising etching the porous
layer.
15. The method of claim 12, wherein forming the porous layer
comprises a vapor deposition process.
16. The method of claim 12, further comprising forming an etch stop
layer between the surface of the imprint lithography template and
the porous layer.
17. The method of claim 12, further comprising forming a seal layer
on the surface of the porous layer.
18. The method of claim 17, further comprising forming a cap layer
on a surface of the seal layer.
19. The method of claim 12, further comprising forming a marker
region between the surface of the imprint lithography template and
the porous layer.
20. The method of claim 12, further comprising chemical-mechanical
planarization of the porous layer.
21. The method of claim 12, wherein the porosity of the porous
layer is non-uniform.
22. A method of forming a layer on an imprint lithography template,
the method comprising: positioning an imprint lithography template
defining a multiplicity of pores in a vacuum chamber; evacuating
the chamber a first time; purging the chamber with a first inert
gas; evacuating the chamber a second time; saturating the chamber
and the imprint lithography template with a second inert gas;
introducing a silicon-containing gas and one or more other gases
into the chamber; and initiating a plasma process to deposit a
silicon-containing layer on the surface of the imprint lithography
template.
23. An imprint lithography template comprising: a first layer; a
second layer, wherein the second layer is a patterned layer of an
imprint lithography template; and two or more intermediate layers
positioned between the first layer and the second layer, wherein at
least one of the intermediate layers is a porous layer and at least
one of the intermediate layers is a stress relief layer configured
to reduce a force acting on the porous intermediate layer.
24. An imprint lithography template comprising: a first layer; a
second layer, wherein the second layer is a patterned layer of an
imprint lithography template; and an intermediate layer positioned
between the first layer and the second layer, wherein the
intermediate layer is configured to reduce a force acting on the
patterned second layer.
25. An imprint lithography template comprising: a first layer; a
second layer; and an intermediate layer positioned between the
first layer and the second layer of the imprint lithography
template, wherein the intermediate layer is configured to allow
assessment of a thickness of the second layer based on a difference
in physical properties between the intermediate layer and the
second layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e)(1) of U.S. Provisional Application Ser. Nos.
61/107,720, filed Oct. 23, 2008; 61/110,051, filed Oct. 31, 2008;
and 61/227,395, filed Jul. 21, 2009, all of which are hereby
incorporated by reference herein.
TECHNICAL FIELD
[0002] The present invention relates to high-throughput
nano-imprint lithography templates, and fabrication thereof.
BACKGROUND
[0003] Nano-fabrication includes the fabrication of very small
structures that have features on the order of 100 nanometers or
smaller. One application in which nano-fabrication has had a
sizeable impact is in the processing of integrated circuits. The
semiconductor processing industry continues to strive for larger
production yields while increasing the circuits per unit area
formed on a substrate; therefore nano-fabrication becomes
increasingly important. Nano-fabrication provides greater process
control while allowing continued reduction of the minimum feature
dimensions of the structures formed. Other areas of development in
which nano-fabrication has been employed include biotechnology,
optical technology, mechanical systems, and the like.
SUMMARY
[0004] In one aspect, an imprint lithography template includes a
porous material defining a multiplicity of pores with an average
pore size of at least about 0.4 nm. The porous material includes
silicon and oxygen. A refractive index of the porous material is
between about 1.4 and about 1.5, and a ratio of Young's modulus (E)
to relative density of the porous material with respect to fused
silica (p.sub.porous/p.sub.fused silica) is at least about
10:1.
[0005] Implementations may include one or more of the following
features. For example, the Young's modulus of the porous material
may be at least about 2 GPa, at least about 5 GPa, at least about
10 GPa, or at least about 20 GPa. The relative density of the
porous material with respect to fused silica may be at least about
50% or at least about 65%. The porous material may include
SiO.sub.xi and 1.ltoreq..times..ltoreq.2.5. The pores may be
substantially closed or interconnected. Interconnected pores may
form channels in the porous material.
[0006] In some cases, the template further includes a base layer
and a cap layer, and the porous material forms a layer between the
base layer and the cap layer. The cap layer may be porous. The cap
layer may be etched or patterned such that protrusions extend from
a surface of the cap layer. The base layer may include fused
silica. Stress in the porous material may be neutral to
compressive. The porosity of the porous material, or porous layer,
may be non-uniform or asymmetric. The porous material may have a
non-uniform porosity gradient. A non-uniform porous layer may be
achieved by changing one or more parameters during the formation of
a porous layer. The parameter to be changed may be a vapor
deposition process parameter. A vapor deposition process may
include atomic layer deposition. In some cases, an imprint
lithography template may include one or more layers (e.g., an
adhesion layer) between the base layer and the porous layer.
[0007] The porosity of a porous layer (e.g., between a base layer
and a cap layer) may range from about 0.1% to about 60% (e.g.,
about 1% to about 20%, or about 5% to about 15%). In some cases,
the porosity of a porous layer may be at least about 10%, or at
least about 20%. The porosity of a cap layer may range from about
0.1% to about 20% (e.g., from about 1% to about 20%, or from about
3% to about 15%).
[0008] The template may further include a seal layer adhered to the
cap layer. The seal layer may be is permeable to helium gas in
contact with the seal layer and substantially impermeable to
species larger than helium. The seal layer may include silicon
oxide. The seal layer may be positioned between the porous layer
and the cap layer. The seal layer may be conformal and/or uniform
in thickness. A thickness of the seal layer may be less than about
10 nm, less than about 5 nm, less than about 3 nm, or about twice
the pore radius. In some cases, the seal layer may be selected to
interact with a mold release agent.
[0009] In another aspect, forming an imprint lithography template
includes forming a layer of porous material on a surface of an
imprint lithography template. The porous layer defines a
multiplicity of pores with an average pore size of at least about
0.4 nm. The porous material includes oxygen and silicon. A
refractive index of the porous material is between about 1.4 and
about 1.5, and a ratio of Young's modulus (E) to relative density
of the porous material with respect to fused silica
(p.sub.porous/p.sub.fused silica) is at least about 10:1.
[0010] In some implementations, as second layer may be formed on
the porous layer. In some cases, the porous layer may be etched to
form a patterned layer. Forming the porous layer may include
etching the porous layer. Forming the porous layer may include a
vapor deposition process, such as plasma enhanced chemical vapor
deposition. The porosity of the porous layer may be substantially
uniform or non-uniform. For example, the porosity may be
asymmetric, or the porosity gradient may be non-uniform, such that
a portion of the layer to be etched is less porous than other
portions of the layer.
[0011] An etch stop layer may be formed between the surface of the
imprint lithography template and the porous layer. A seal layer may
be formed on the surface of the porous layer. A cap layer may be
formed on a surface of the seal layer. Alternatively, a cap layer
may be formed on the porous layer, and a seal layer may be formed
on the cap layer. In some cases, the porous layer is etched to form
a patterned layer. A marker region may be formed between the
surface of the imprint lithography template and the porous layer.
The marker region may serve as a thin film optical metrology marker
on the base layer. In some cases, a region of a base layer may be
masked while forming the porous layer to create a recess in the
porous layer form film thickness metrology. In some cases, a porous
layer (e.g., an intermediate porous layer or a porous cap layer)
may be polished, for example, using a chemical-mechanical
planarization process. In some cases, a mesa may be etched in a
porous layer or a base layer.
[0012] In another aspect, forming a layer on an imprint lithography
template includes positioning an imprint lithography template
defining a multiplicity of pores in a vacuum chamber, evacuating
the chamber a first time, purging the chamber with a first inert
gas, and evacuating the chamber a second time. The chamber may then
be saturated with a second inert gas. A silicon-containing gas and
one or more other gases may be introduced into the chamber, and a
plasma process may be initiated to deposit a silicon-containing
layer on the surface of the imprint lithography template. This
process substantially fills pores in the porous layer of the
imprint lithography template with an inert gas before the
silicon-containing layer is deposited on the porous layer. With the
pores in the porous layer filled with inert gas, reactants used to
form the silicon-containing layer are inhibited from diffusing into
the porous layer and clogging the pores, changing the chemical and
physical nature of the porous layer. Thus, the porous layer remains
substantially uniform, and does not become more dense near the
silicon-containing layer.
[0013] In one aspect, an imprint lithography template includes a
first layer and a second layer. The second layer is a patterned
layer of an imprint lithography template. Two or more intermediate
layers are positioned between the first layer and the second layer.
At least one of the intermediate layers is a porous layer and at
least one of the intermediate layers is a stress relief layer
configured to reduce a force acting on the porous intermediate
layer. In another aspect, an imprint lithography template includes
a first layer, a second layer, and an intermediate layer positioned
between the first layer and the second layer. The second layer is a
patterned layer of an imprint lithography template, and the
intermediate layer is configured to reduce a force acting on the
patterned second layer. In another aspect, an imprint lithography
template includes a first layer and one or more layers on the first
layer. At least one of the one or more layers is porous. A stress
relief layer may be positioned on the back side of the template to
counter a force produced by the layer or layers on the first
layer.
[0014] In some implementations, the first layer is a base layer and
the second layer is a top layer. The top layer may be a cap layer.
The stress relief layer provides a compressive force, and the
compressive force reduces a tensile force acting on the porous
intermediate layer. In other implementations, the stress relieve
layer provides a tensile force, and the tensile force reduces a
compressive force acting on the porous intermediate layer. In some
cases, a neutral to compressive stress state is maintained in the
porous intermediate layer during static and dynamic conditions,
such as template bending during separation.
[0015] The porous intermediate layer may be positioned between two
stress relief layers, the stress relief layer may be positioned
between two porous intermediate layers, or any combination thereof.
The stress relief layer may include a metal, metal oxide, metal
nitride, or metal carbide. In some cases, the stress relief layer
is porous (i.e., more porous or less dense than fused silica).
[0016] In one aspect, an imprint lithography template includes a
first layer, a second layer, and an intermediate layer positioned
between the first layer and the second layer of the imprint
lithography template. The intermediate layer is configured to allow
assessment of a thickness of the second layer based on a difference
in physical properties between the intermediate layer and the
second layer.
[0017] In some implementations, the first layer is a base layer and
the second layer is a top layer or a cap layer. The intermediate
layer may an etch stop layer. The intermediate layer may include a
metal, metal oxide, metal carbide, or metal nitride. The
intermediate layer may provide stress relief for the top layer. The
physical property may be an optical property, such as transmittance
or reflectance. In some cases, the intermediate layer is
non-continuous. That is, the intermediate layer may include one or
more separate regions (e.g., marker regions). A thickness of the
intermediate layer may be less than about 30 nm, less than about 20
nm, less than about 10 nm, less than about 5 nm, or less than about
3 nm. Thus, the intermediate layer, even if discontinuous, may not
introduce a noticeable perturbation to the second layer. In some
cases, the second lay may be polished to form a substantially
smooth surface. When marker regions are used, the regions may be
located outside of the area occupied by the mesa or patterned
portion of an imprint lithography template.
[0018] Aspects and implementations described herein may be combined
in ways other than described above. Other aspects, features, and
advantages will be apparent from the following detailed
description, the drawings, and the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 illustrates a simplified side view of a lithographic
system.
[0020] FIG. 2 illustrates a simplified side view of the substrate
shown in FIG. 1 having a patterned layer positioned thereon.
[0021] FIG. 3 illustrates a side view of a gas pocket trapped
between a substrate and a template.
[0022] FIG. 4 illustrates a side view of a template with a porous
layer.
[0023] FIG. 5 illustrates a template with an asymmetric porous
layer.
[0024] FIG. 6 illustrates a unitary porous template.
[0025] FIG. 7 illustrates a porous template with no base layer.
[0026] FIG. 8A illustrates a porous template with a sealed cap
layer.
[0027] FIG. 8B illustrates a porous template with a sealed porous
layer.
[0028] FIG. 9 is a flow chart for a process to form a cap layer on
a porous layer with reduced clogging of pores in the porous
layer.
[0029] FIG. 10 illustrates forming a cap layer on a porous layer
with reduced clogging of the porous layer.
[0030] FIG. 11 illustrates a side view of a template with tensile
stress associated with a porous layer.
[0031] FIG. 12 illustrates a side view of a template with a porous
layer and a relief layer.
[0032] FIGS. 13A and 13B illustrate side views of a template with a
porous layer and multiple relief layers.
[0033] FIG. 14 illustrates a side view of a template with multiple
porous layers and multiple relief layers.
[0034] FIGS. 15A and 15B illustrate reduction of stress on a
nano-imprint lithography template with the addition of a stress
relief layer opposite the mold.
[0035] FIG. 16 illustrates a nano-imprint lithography template with
an etch stop layer.
[0036] FIGS. 17A and 17B illustrate a nano-imprint lithography
template with a marker region for use as a metrology marker.
[0037] FIGS. 18A and 18B are photographs that show spreading of
imprint resist between a substrate and a template with a porous
intermediate layer.
[0038] FIGS. 19A, 19B, and 19C are photographs that show spreading
of imprint resist between a substrate and a template without a
porous layer.
[0039] FIGS. 20A and 20B are photographs that show rapid wicking of
imprint resist into a porous template.
[0040] FIGS. 21A and 21B are photographs that show slow wicking of
imprint resist into a template with a porous layer and a cap
layer.
[0041] FIGS. 22A through 22D are photographs that show filling of
voids between droplets in contact with a template as the droplets
spread.
DETAILED DESCRIPTION
[0042] An exemplary nano-fabrication technique in use today is
commonly referred to as imprint lithography. Exemplary imprint
lithography processes are described in detail in numerous
publications, such as U.S. Patent Application Publication No.
2004/0065976, U.S. Patent Application Publication No. 2004/0065252,
and U.S. Pat. No. 6,936,194, all of which are hereby incorporated
by reference herein.
[0043] An imprint lithography technique disclosed in each of the
aforementioned U.S. patent application publications and patent
includes formation of a relief pattern in a formable
(polymerizable) layer and transferring a pattern corresponding to
the relief pattern into an underlying substrate. The substrate may
be coupled to a motion stage to obtain a desired positioning to
facilitate the patterning process. The patterning process uses a
template spaced apart from the substrate and the formable liquid
applied between the template and the substrate. The formable liquid
is solidified to form a rigid layer that has a pattern conforming
to a shape of the surface of the template that contacts the
formable liquid. After solidification, the template is separated
from the rigid layer such that the template and the substrate are
spaced apart. The substrate and the solidified layer are then
subjected to additional processes to transfer a relief image into
the substrate that corresponds to the pattern in the solidified
layer.
[0044] Referring to FIG. 1, illustrated therein is a lithographic
system 10 used to form a relief pattern on substrate 12. An imprint
lithography stack may include substrate 12 and one or more layers
(e.g., an adhesion layer) adhered to the substrate. Substrate 12
may be coupled to substrate chuck 14. As illustrated, substrate
chuck 14 is a vacuum chuck. Substrate chuck 14, however, may be any
chuck including, but not limited to, vacuum, pin-type, groove-type,
electromagnetic, and the like, or any combination thereof.
Exemplary chucks are described in U.S. Pat. No. 6,873,087, which is
hereby incorporated by reference herein.
[0045] Substrate 12 and substrate chuck 14 may be further supported
by stage 16. Stage 16 may provide motion about the x-, y-, and
z-axes. Stage 16, substrate 12, and substrate chuck 14 may also be
positioned on a base (not shown).
[0046] Spaced-apart from substrate 12 is a template 18. Template 18
may include a mesa 20 extending therefrom towards substrate 12,
mesa 20 having a patterning surface 22 thereon. Further, mesa 20
may be referred to as mold 20. Template 18 and/or mold 20 may be
formed from such materials including, but not limited to,
fused-silica, quartz, silicon, organic polymers, siloxane polymers,
borosilicate glass, fluorocarbon polymers, metal, hardened
sapphire, and the like, or any combination thereof. As illustrated,
patterning surface 22 comprises features defined by a plurality of
spaced-apart recesses 24 and/or protrusions 26, though embodiments
of the present invention are not limited to such configurations.
Patterning surface 22 may define any original pattern that forms
the basis of a pattern to be formed on substrate 12.
[0047] Template 18 may be coupled to chuck 28. Chuck 28 may be
configured as, but not limited to, vacuum, pin-type, groove-type,
electromagnetic, and/or other similar chuck types. Exemplary chucks
are further described in U.S. Pat. No. 6,873,087, which is hereby
incorporated by reference herein. Further, chuck 28 may be coupled
to imprint head 30 such that chuck 28 and/or imprint head 30 may be
configured to facilitate movement of template 18.
[0048] System 10 may further comprise a fluid dispense system 32.
Fluid dispense system 32 may be used to deposit polymerizable
material 34 on substrate 12. Polymerizable material 34 may be
positioned upon substrate 12 using techniques such as drop
dispense, spin-coating, dip coating, chemical vapor deposition
(CVD), physical vapor deposition (PVD), thin film deposition, thick
film deposition, and the like, or any combination thereof.
Polymerizable material 34 (e.g., imprint resist) may be disposed
upon substrate 12 before and/or after a desired volume is defined
between mold 20 and substrate 12 depending on design
considerations. Polymerizable material 34 may include components as
described in U.S. Pat. No. 7,157,036 and U.S. Patent Application
Publication No. 2005/0187339, both of which are hereby incorporated
by reference herein.
[0049] Referring to FIGS. 1 and 2, system 10 may further comprise
an energy source 38 coupled to direct energy 40 along path 42.
Imprint head 30 and stage 16 may be configured to position template
18 and substrate 12 in superimposition with path 42. System 10 may
be regulated by a processor 54 in communication with stage 16,
imprint head 30, fluid dispense system 32, source 38, or any
combination thereof, and may operate on a computer readable program
stored in memory 56.
[0050] Either imprint head 30, stage 16, or both may alter a
distance between mold 20 and substrate 12 to define a desired
volume therebetween that is substantially filled by polymerizable
material 34. For example, imprint head 30 may apply a force to
template 18 such that mold 20 contacts polymerizable material 34.
After the desired volume is substantially filled with polymerizable
material 34, source 38 produces energy 40, e.g., broadband
ultraviolet radiation, causing polymerizable material 34 to
solidify and/or cross-link conforming to shape of a surface 44 of
substrate 12 and patterning surface 22, defining a patterned layer
46 on substrate 12. Patterned layer 46 may include a residual layer
48 and a plurality of features shown as protrusions 50 and
recessions 52, with protrusions 50 having a thickness t.sub.1 and
residual layer 48 having a thickness t.sub.2.
[0051] The above-described system and process may be further
implemented in imprint lithography processes and systems referred
to in U.S. Pat. No. 6,932,934, U.S. Patent Application Publication
No. 2004/0124566, U.S. Patent Application Publication No.
2004/0188381, and U.S. Patent Application Publication No.
2004/0211754, all of which are hereby incorporated by reference
herein.
[0052] In nano-imprint processes in which polymerizable material is
applied to a substrate by drop dispense or spin coating methods,
gases may be trapped inside recesses in the template after the
template contacts the polymerizable material. In nano-imprint
processes in which polymerizable material is applied to a substrate
by, drop dispense methods, gases may also be trapped between drops
of polymerizable material or imprint resist dispensed on a
substrate (e.g., on an imprinting stack). That is, gases may be
trapped in interstitial regions between drops as the drops
spread.
[0053] Gas escape and dissolution rates may limit the rate at which
the polymerizable material is able to form a continuous layer on
the substrate or the rate at which the polymerizable material is
able to fill template features after the template contacts the
polymerizable material, thereby limiting throughput in nano-imprint
processes. For example, a substrate or a template may be
substantially impermeable to a gas trapped between the substrate
and the template. In some cases, a polymeric layer adhered to the
substrate or the template may become saturated with gas, such that
gas between the imprinting stack and the template is substantially
unable to enter the saturated polymeric layer, and remains trapped
between the template and the substrate. Gas that remains trapped
between the template and the substrate may cause filling defects in
the patterned layer.
[0054] FIG. 3 illustrates gas (or gas pocket) 60 in patterned layer
46 between substrate 12 and template 18. The gas 60 may include,
but is not limited to, air, nitrogen, carbon dioxide, helium, or
the like. Gas 60 between substrate 12 and template 18 may result in
pattern distortion of features formed in patterned layer 46, low
fidelity of features formed in patterned layer 46, non-uniform
thickness of residual layer 48 across patterned layer 46, or the
like.
[0055] In an imprint lithography process, gas trapped between the
substrate and the template may escape through the polymerizable
material, the substrate, or the template. The amount of gas that
escapes through any medium may be influenced by the contact area
between the trapped gas and the medium. The contact area between
the trapped gas and the polymerizable material may be less than the
contact area between the trapped gas and the substrate or the
template. For example, a thickness of the polymerizable material on
a substrate may be less than about 1 .mu.m, or less than about 100
nm. In some cases, a polymerizable material may absorb enough gas
to become saturated with the gas before imprinting, such that
trapped gas is substantially unable to enter the polymerizable
material. In contrast, the contact area between the trapped gas and
the substrate or the template may be relatively large.
[0056] The gas permeability of a medium may be expressed as
P=D.times.S, in which P is the permeability, D is the diffusion
coefficient, and S is the solubility. In a gas transport process, a
gas adsorbs onto a surface of the medium, and a concentration
gradient is established within the medium. The concentration
gradient may serve as the driving force for diffusion of gas
through the medium. Gas solubility and the diffusion coefficient
may vary based on, for example, packing density of the medium.
Adjusting a packing density of the medium may alter the diffusion
coefficient and hence the permeability of the medium.
[0057] For a multi-layer film, effective permeability may be
calculated from a resistance model, such as an analog of an
electric circuit described by F. Peng, et al. in J. Membrane Sci.
222 (2003) 225-234 and A. Ranjit Prakash et al. in Sensors and
Actuators B 113 (2006) 398-409, which are both hereby incorporated
by reference herein. The resistance of a material to the permeation
of a vapor is defined as the permeance resistance, R.sub.p. For a
two-layer composite film with layer thicknesses l.sub.1 and
l.sub.2, and corresponding permeabilities P.sub.1 and P.sub.2,
permeance resistance may be defined as:
R p = .DELTA. p J = 1 ( P / l ) A ( 1 ) ##EQU00001##
in which .DELTA.p is the pressure difference across the film, J is
the flux, and A is the area. The resistance model predicts
R.sub.p=R.sub.1+R.sub.2 (2)
When the cross-sectional area is the same for both materials 1 and
2, equation (2) may be rewritten as:
l 1 + l 2 P = l 1 P 1 + l 2 P 2 ( 3 ) ##EQU00002##
[0058] A gas may be thought of as having an associated kinetic
diameter. The kinetic diameter provides an idea of the size of the
gas atoms or molecules for gas transport properties. D. W. Breck,
Zeolite Molecular Sieves--Structure, Chemistry, and Use, John Wiley
& Sons, New York, 1974, p. 636, which is incorporated by
reference herein, lists the kinetic diameter for helium (0.256 nm),
argon (0.341 nm), oxygen (0.346 nm), nitrogen (0.364 nm), and other
common gases.
[0059] In some imprint lithography processes, a helium purge is
used to substantially replace air between the template and the
substrate or imprinting stack with helium gas. To simplify the
comparison between a helium environment and an air environment in
an imprint lithography process, the polar interaction between
oxygen in air and silica may be disregarded by Modeling air as pure
argon. Both helium and argon are inert gases, and argon has a
kinetic diameter similar to that of oxygen. Unlike oxygen, however,
helium and argon do not interact chemically with fused silica or
quartz (e.g., in a template or substrate).
[0060] Internal cavities (solubility sites) and structural channels
connecting the solubility sites allow a gas to permeate through a
medium. The gas may be retained in the solubility sites. The size
of the internal cavities and the channel diameter relative to the
size (or kinetic diameter) of the gas influence the rate at which
the gas permeates the medium.
[0061] The sizes of individual interstitial solubility sites of
fused silica have been shown to follow a log-normal distribution by
J. F. Shackelford, "Gas solubility in glasses--principles and
structural implications," J. Non-Cryst. Solids 253(1999): 231-241,
which is incorporated by reference herein. As indicated by the
interstitial diameter distribution (mode=0.181 nm; mean=0.196 nm)
and the kinetic diameter of helium and argon, the number of fused
silica solubility sites available to helium exceeds the number of
solubility sites available to argon. The total number of
interstitial sites is estimated to be 2.2.times.10.sup.28 per
m.sup.3, with 2.3.times.10.sup.27 helium solubility sites per
m.sup.3 and 1.1.times.10.sup.26 argon solubility sites per m.sup.3.
The average distance between solubility sites for helium is
considered to be 0.94 nm, while the average distance between
solubility sites for argon is considered to be 2.6 nm. The
structural channels connecting these solubility sites are thought
to be similar to the helical arrangement of 6-member Si--O rings,
with a diameter of about 0.3 nm. Table 1 summarizes some parameters
affecting helium and argon permeability in fused silica.
TABLE-US-00001 TABLE 1 Selected properties of helium and argon.
Property Helium Argon Kinetic Diameter (nm) 0.256 0.341 Solubility
Site Density (m.sup.-3) 2.3 .times. 10.sup.27 1.1 .times. 10.sup.26
Distance Between Solubility Sites (nm) 0.94 2.6 Structural Channel
Diameter ~0.3 ~0.3 Connecting Solubility Sites (nm)
[0062] Boiko et al., "Migration Paths of Helium in .alpha.-Quartz
and Vitreous Silica from Molecular Dynamics Data," Glass Physics
and Chemistry 29(2003): 42-48, which is incorporated by reference
herein, describes behavior of helium in amorphous or vitreous
silica. Within a solubility site, the helium atom vibrates at an
amplitude allowed by the interstitial volume. The atom passes from
interstice to interstice through channels, which may be smaller in
diameter than the interstices.
[0063] The parameters listed in Table 1 indicate that argon
permeability in fused silica may be very low or negligible at room
temperature (i.e., the kinetic diameter of argon exceeds the fused
silica channel size). Since the kinetic diameters of oxygen and
nitrogen are larger than the kinetic diameter of argon, air may be
substantially unable to permeate fused silica. On the other hand,
helium may diffuse into and permeate fused silica. Thus, when a
helium environment is used rather than ambient air for a
nano-imprint process, helium trapped between the template and the
substrate may be able to permeate a fused silica template.
[0064] The relative porosity of similar materials may be defined as
a relative difference in density of the materials. For example, a
relative porosity of spin on glass (SOG) (density p.sub.SOG=1.4
g/cm.sup.3) with respect to fused silica (density p.sub.fused
silica=2.2 g/cm.sup.3) may be calculated as 100%.times.(p.sub.fused
silica)/p.sub.fused silica, or 64%. Fused silica may be used as a
reference material for other materials with oxygen-silicon bonds.
For material used to form a porous layer in an imprint lithography
template, a relative density of a material with respect to fused
silica of at least about 50% or at least about 65% provides a
porosity suitable to allow movement of gases
[0065] In some cases, porogens may be added to material used to
form a portion of a template or a substrate to increase a porosity
and pore size of the material. Porogens include, for example,
organic compounds that may be vaporized, such as norbornene,
.alpha.-terpinene, polyethylene oxide, and polyethylene
oxide/polypropylene oxide copolymer, and the like, and any
combination thereof. Porogens may be, for example, linear or
star-shaped. Porogens and process conditions may be selected to
form a microporous low-k porous layer, for example, with an average
pore diameter of less than about 2 nm, thereby increasing the
number of solubility sites for a range of gases. In addition, the
introduction of porogens and the increased porosity may enlarge the
structure channels connecting gas solubility sites. For pore sizes
of about 0.4 nm or greater, helium permeability of a low-k film may
exceed helium permeability of vitreous fused silica.
[0066] One method of removing gases 60 from the volume defined
between substrate 12 and template 18 includes absorption of gases
60 through template 18. In some cases, as illustrated in FIG. 4,
template 18 may be modified to include one or more layers formed on
a base layer 62. For example, first layer 64 may be formed on base
layer 62, and second layer 63 may be formed on first layer 64. When
a template includes a base layer 62, a first layer 64, and a second
layer 63, the first layer may be referred to as the intermediate
layer, and the second layer may be referred to as the cap layer.
When a template includes a base layer 62 and three or more
additional layers, the top layer may be referred to as the cap
layer and the layers between the base layer and the cap layer may
be referred to as intermediate layers.
[0067] As noted above with respect to template 18, base layer 62
may be formed from materials including, but not limited to, fused
silica, quartz, silicon, organic polymers, siloxane polymers,
borosilicate glass, fluorocarbon polymers, metal, hardened
sapphire, and the like, or any combination thereof. A cap layer,
one or more intermediate layers, or any combination thereof may be
a porous layer. As used herein, "porous layer" refers to a layer
that is less dense and/or more porous than fused silica.
[0068] As used herein, a thickness of a cap layer is considered to
be a thickness of the residual layer (i.e., not including the
height of the protrusions). Gas may diffuse more quickly through
portions of the cap layer from which there are no protrusions,
achieving an overall increase in helium permeability. Thus, cap
layers with thinner residual layers allow more rapid diffusion of
gas through the cap layer and into the next (e.g., porous) layer.
This diffusion rate depends at least in part on the fraction of the
surface area of the template free from protrusions. Intermediate
layers and cap layers may be formed by a vapor deposition process
such as plasma enhanced chemical vapor deposition. Ranges of
process variables for forming intermediate layers and cap layers
are listed in Table 2 below.
TABLE-US-00002 TABLE 2 Example PECVD process variables for
intermediate and cap layers. PECVD process variable Cap layer First
layer/intermediate layer N.sub.2O:SiH.sub.4 Ratio 2-25 1-3 Power
Density (W/cm.sup.2) 0.1-0.25 0.15-0.5 Pressure (mTorr) 300-1000
100-500 Temperature (.degree. C.) 250-450 Room temp. to 350
[0069] Porosities of the cap layer and the intermediate layer may
be selected to facilitate transportation of gases 60 trapped
between the substrate 12 and the template through the cap layer and
into the intermediate layer. For example, a cap layer may be
microporous, mesoporous, or a combination thereof. That is, the
pores in the cap layer may be less than 2 nm in diameter
(microporous) or between 2 nm and 50 nm in diameter (mesoporous).
An intermediate layer may be microporous, mesoporous, or
macroporous. That is, pores in an intermediate layer may be less
than 2 nm in diameter (microporous), from 2 nm to 50 nm in diameter
(mesoporous), or greater than 50 nm in diameter (macroporous). In
some cases, an intermediate layer may have regions with different
porosities. For example, an intermediate layer may have a
microporous region and a mesoporous region. Porous layers are
described in U.S. patent application Ser. No. 12/275,998, which is
incorporated herein by reference.
[0070] Sizes of the pores in a porous cap layer or porous
intermediate layer may be substantially uniform, or with a desired
distribution. Pores may range from substantially closed to fully
interconnected. In some cases, for a cap layer, a pore size or
average pore size is at least about 0.4 nm, at least about 0.5 nm,
or less than about 2 nm (e.g., less than about 1 nm, in a range
between about 0.4 nm and about 1 nm, or in a range between about
0.4 nm and about 0.8 nm). For an intermediate layer, pore size or
average pore size may be at least about 0.4 nm or at least about
0.5 nm (e.g., up to about 1 nm, up to about 2 nm, up to about 15
nm, up to about 30 nm, up to about 40 nm, up to about 50 nm, or
larger than about 50 nm).
[0071] For template 18 with a cap layer of SiO.sub.x (thickness of
about 10 nm and permeability P.sub.1), template permeability may be
adjusted by selecting porosity and pore size of one or more
intermediate layers. The effect of the permeability and thickness
of the intermediate layers(s) on the effective permeability of a
multi-layer composite imprinting stack with a thickness of 310 nm
is shown in Table 3.
TABLE-US-00003 TABLE 3 Intermediate layer properties for
multi-layer composites. Cap Layer Intermediate Base Layer Effective
Thickness (SiO.sub.x), layer Thickness, Thickness (SiO.sub.2),
Permeability Permeability of Permeability P.sub.1 Permeability
P.sub.2 Permeability P.sub.1 Ratio the Total Stack 10 nm 300 nm 0
P.sub.2 = 1000 P.sub.1 30.1 P.sub.1 10 nm 200 nm 100 nm P.sub.2 =
1000 P.sub.1 2.8 P.sub.1 10 nm 100 nm 200 nm P.sub.2 = 1000 P.sub.1
1.5 P.sub.1 10 nm 300 nm 0 P.sub.2 = 100 P.sub.1 23.8 P.sub.1
[0072] Table 3 suggests that increasing a thickness of the
intermediate layer alone may yield a higher effective permeability
than increasing the permeability of the intermediate layer alone.
That is, for composite imprinting stacks with a total thickness of
310 nm and having an intermediate layer thickness of 100 nm, 200
nm, or 300 nm and a cap layer thickness of 10 nm, the effective
permeability increases twenty-fold, from 1.5 P.sub.1 to 2.8 P.sub.1
to 30.1 P.sub.1, respectively, over the 200 nm increase in
intermediate layer thickness. For an intermediate layer thickness
of 300 nm and a cap layer thickness of 10 nm, a ten-fold increase
in permeability of the intermediate layer from 100 P.sub.1 to 1000
P.sub.1 increases the effective permeability from 23.8 P.sub.1 to
30.1 P.sub.1.
[0073] In some cases, as shown in FIG. 5, an imprint lithography
template may include a base layer and a first layer. The first
layer may be a porous layer. The first layer may be patterned, and
may be thought of as a cap layer. Referring to FIG. 5, a porous
layer 61 can be formed on a base layer 62. Porosity of the porous
layer 61 may be non-uniform or asymmetric, as shown in FIG. 5, or
substantially uniform. Porous layer 61 may be a cap layer. In some
cases, porous layer 61 may have a porosity gradient, shown by the
distribution of pores 65, such that the density of the layer is
higher near the top surface of the layer (i.e., the surface in
contact with the imprint resist during use). The porosity gradient
may include changes in average pore size, pore size distribution,
and/or pore density. The gradient may improve the mechanical
strength of the features that are etched directly into the porous
layer, while allowing diffusion of gases into the porous layer.
That is, reduced porosity near the top of the cap layer (e.g.,
reduced porosity of the protrusions and proximate the protrusions)
may yield a patterned portion with more mechanical strength than a
cap layer with a higher porosity near the top of the cap layer. In
some cases, the porous layer 61 may have a substantially uniform
density in the portion of the layer that is etched to form the
protrusions and recessions. The porous layer 61 may have
microporous, mesoporous, or macroporous regions, or any combination
thereof.
[0074] As shown in FIG. 6, a template 18 may be formed as a unitary
structure with a porosity and average pore size selected to allow
efficient diffusion of a gas while maintaining mechanical strength
near the top of the cap layer. Templates made from, for example,
organic polymers, inorganic materials (e.g., silicon carbide, doped
silica, VYCOR.RTM.), and the like, or any combination thereof, may
have a lower packing density, and therefore a higher gas (e.g.,
helium) permeability, than vitreous fused silica. Template 18
consists essentially of a single porous layer. The porous layer is
not adhered to a base layer. Template 18 may be smooth or
patterned. Template 18 may be an asymmetric porous layer, as shown
in FIG. 6, or a symmetric porous layer.
[0075] As shown in FIG. 7, a template 18 may include a first layer
64 and a second layer 63. First layer 64 may be a porous layer.
Second layer 63 may be a cap layer. As with template 18 in FIG. 6,
the first layer is not adhered to a base layer. The second layer 63
may inhibit penetration of the polymerizable material into the
porous material. The second layer 63 may also impart desirable
surface properties, mechanical properties, and the like to the
template. Template 18 may be smooth or patterned. First layer 64
may be an asymmetric porous layer.
[0076] Microporous layers may be advantageous in imprint
lithography applications. For example, microporous layers may have
pores large enough to allow diffusion of trapped gas through the
pores, but small enough to inhibit penetration of the pores by
polymerizable fluid or other substances. Microporous cap layers may
have sufficient mechanical strength to withstand repeated use
without cracking, buckling, or delaminating. Compared to patterned
mesoporous and macroporous layers, patterned microporous layers may
have smoother sidewalls and smaller void defects inside etched
features.
[0077] In some cases, pores at a surface of a template (e.g., in a
cap layer or other porous layer), if not sealed, may allow
penetration of polymerizable fluid or other substances into the
template, which may cause clogging of the pores or added stress
during an imprinting process. If pores near a surface of a template
are sufficiently small, sealing of the pores may not be needed to
inhibit penetration of polymerizable fluid or other substances into
the pores. In some cases, however, it is advantageous to seal or
fill exposed pores (e.g., with a less porous silicon oxide layer)
by using a thin film deposition method that produces substantially
continuous, conformal, ultrathin gas-permeable films to inhibit
disadvantageous penetration, clogging, saturation, and the like, of
the template by polymerizable fluid or other substances. Pore
sealing may be accomplished by a number of methods including, but
not limited to, vapor-based film deposition processes such as
chemical vapor deposition (CVD), atomic layer deposition (ALD),
plasma-assisted atomic layer deposition (PA-ALD), pulsed
plasma-enhanced chemical vapor deposition (pulsed-PECVD), molecular
layer deposition (MLD), and physical vapor deposition (PVD), or by
solution-based film deposition methods such as dip coating and spin
coating, or plasma treatment. PA-ALD is described in US patent
Application Publication No. US 2007/0190777, which is incorporated
herein by reference. Pulsed-PECVD is described in U.S. Patent
Application Publication No. 2008/0199632, which is incorporated
herein by reference.
[0078] The selection of a seal layer deposition process and film
composition can depend on several factors, including the size
and/or geometry of template protrusions and recesses, the exposed
pore diameter in the porous film, the desired permeability and
mechanical properties of the seal layer, and the ability of the
seal layer to interact with release agents, etc.
[0079] FIG. 8A shows a porous template 18 with a base layer 62,
first intermediate layer 64, cap layer 63, and seal layer 59. Seal
layer 59 may be made from materials including, but not limited to:
metal oxides, nitrides, carbides, oxynitrides, oxycarbides, or
polymers such as organo-silanes and polyxylylenes. A thickness of
seal layer 59 on the surface of a porous layer may be less than
about 10 nm, less than about 5 nm, less than about 3 nm, or, in
some cases, about two times greater than the pore radius. In some
cases, the pore sealing deposition method may be selected to
substantially confine the reaction and growth of seal layer 59 to
the surface of the porous layer. In certain cases, the seal layer
reactants may be allowed to penetrate several nanometers into the
porous layer.
[0080] Pore sizes in seal layer 59 may be larger than the kinetic
diameter of the gas in the imprint environment to facilitate the
diffusion of the gas into the adjoining porous layer. Pore sizes in
seal layer 59 may be less than about 2 nm, less than about 0.8 nm,
or less than about 0.6 nm, such that helium is able to diffuse
through the seal layer. Seal layer 59 may be selected such that
atoms or molecules larger than helium, oxygen, nitrogen, or carbon
dioxide may be unable to diffuse through the seal layer. The
material used to form seal layer 59 may be selected to withstand
repeated use in nano-imprint lithography processes, including
piranha, dilute base, ozone, or plasma cleaning processes. In some
cases, seal layer 59 may be selected to be a non-permanent or
sacrificial layer which is intended to be removed and replaced.
[0081] FIG. 8B illustrates a porous template 18 with a base layer
62, porous intermediate layer 64, seal layer 59, and cap layer 63.
The seal layer preferably has pores large enough for helium to pass
through, but small enough to substantially block reactive species
in vapor or liquid phase from penetrating the porous layer during
cap layer deposition. Seal layer 59 may have a thickness of about 1
nm to about 10 nm, or less than about 5 times the pore radius, less
than about 3 times the pore radius, or about two times the pore
radius. Seal layer 59 may include, for example, silicon oxide
(SiO.sub.x). In some cases, rather than seal the surface pores
completely with a continuous film, a seal layer process may be used
to decrease the open pore size of the porous layer.such that
diameters of the pores inhibit the penetration (e.g., diffusion) of
cap layer components into the porous layer.
[0082] The presence of the seal layer beneath the cap layer (e.g.,
between the cap layer and the porous layer) allows a clear
transition from the cap layer to the porous layer, and inhibits
penetration of pore-clogging contaminants into the porous layer.
For example, seal layer 59 may inhibit penetration of reactive
species present during formation of the cap layer 63 into porous
layer 64. Penetration and pore clogging of the porous layer
increases the density of the porous layer near the interface
between the porous layer and, for example, the cap layer, and thus
makes it difficult to ascertain the location of the interface
during etching. The presence of a seal layer below the cap layer
would maintain the integrity of the interface, and reduce or
substantially eliminate ambiguity as to the required etch depth of
the features in the cap layer. Thus, the deposition of a seal layer
on the porous layer enables the etch process, because it is
advantageous to have as little cap layer material between the
bottom of the feature and the porous layer underneath. This
distance is indicated by d in FIG. 8B.
[0083] In an example, a, porous layer is deposited on a base layer.
A thin (e.g., 5 nm), dense pore seal layer is formed on the porous
layer, and a dense cap layer (95 nm) is formed on the seal layer.
The total thickness of the dense coating is 100 nm. If the cap
layer is etched to a depth of 90 nm, then d=10 nm, and 10 nm of
dense film separates the bottom of the feature from the underlying
porous film. In the absence of a seal layer, then several
nanometers of the porous layer may have become blocked and the film
density profile may vary with depth, all of which make it more
difficult to determine how far to etch features in to the cap layer
so that the features reside in a uniformly dense film with a known
distance to the porous layer underneath. Some methods of pore
sealing include ALD, PA-ALD, and pulsed PECVD, as well as other
methods mentioned herein. Use of a method such as ALD to form the
cap layer as well as the seat layer would limit throughput and
increase production costs.
[0084] As described herein, a pore seal layer may allow optical
thickness measurements of the cap layer if the refractive index of
the seal layer differs from the refractive index of the cap layer.
For example, a cap layer may be deposited on top of the seal layer
and then polished back to a known measurable distance from the seal
layer.
[0085] In some cases, a less porous seal layer and a cap layer may
be deposited on a more porous layer (e.g., intermediate layer) at
temperatures less than, equal to, or greater than that used for
deposition of the more porous layer. Although the less porous layer
may be deposited at a higher temperature than that used for the
more porous layer beneath it, it may be desirable in some cases to
deposit the less porous layer at a temperature equal to or less
than the deposition temperature of the more porous layer if thermal
effects during the less porous layer deposition induce undesirable
changes to pore size, pore size distribution, pore
interconnectivity, and the like in the more porous layer.
[0086] The material used to form a porous cap layer or a porous
intermediate layer may be selected to withstand repeated use in
nano-imprint lithography processes, including piranha, dilute base,
and ozone, or plasma cleaning processes. In some cases, a porous
cap layer or a porous intermediate layer may be designed for
limited use, and may not need the ability to withstand a cleaning
process. Adhesion of an intermediate layer to a base layer and to a
cap layer may be, for example, at least about three times the force
required to separate the template from the patterned layer formed
in an imprint lithography process. Material properties to be
considered in selection of porous materials include adhesion to the
base layer, coefficient of thermal expansion, thermal conductivity,
refractive index, and UV light transmittance and absorbance. For
example, a material with low UV absorbance allows UV radiation to
pass through a cap layer or an intermediate layer of a template to
polymerize the imprint resist without generating a disadvantageous
amount of heat proximate the imprint resist. In certain
embodiments, Young's modulus of the porous material may be, for
example, at least about 2 GPa, at least about 5 GPa, at least about
10 GPa, or at least about 20 GPa.
[0087] In some applications, a template will be required to make
hundreds or even thousands of imprints before it has satisfied its
cost of ownership objective, therefore materials used for the
porous layer must have sufficient mechanical strength to survive
this number of imprints without cracking, buckling, or
delaminating. A porous material with a selected Young's modulus, in
combination with a selected relative density and refractive index
may be used to form a porous layer with unexpected advantages,
including a decrease in filling time, allowing high-throughput in a
fabrication process, and a simultaneous ability to withstand
mechanical forces present during the imprinting process. This
combination of desirable properties allows increased process
longevity and low template defectivity.
[0088] The ratio of the Young's modulus of a porous material
including silicon and oxygen to the relative density of that
material with respect to fused silica, is an indicator of the
ability of a porous material to perform as a porous layer in an
imprint lithography template. A porous silicon- and
oxygen-containing material that provides desirable throughput and
durability may have a ratio of Young's modulus to relative density
of the material with respect to fused silica of at least about
10:1, at least about 20:1, or at least about 30:1.
[0089] Optical-based processes related to imprint lithography
templates include, for example, optical-based template pattern
inspection. To facilitate optical-based processes, the refractive
index of a porous layer may be similar to the refractive index of
other layers in the template (e.g., cap layer, seal layer) on the
same template, such that unwanted optical effects (e.g., bending of
light and related distortion) are reduced during processes
including measurement processes and inspection processes. The
refractive index for fused silica is 1.46. When fused silica is
used as a base, it may be desirable for other layers of an imprint
lithography template to have a refractive index close to that of
fused silica. For increased optical compatibility with other layers
in an imprint lithography template, the refractive index of a
porous layer in an imprint lithography template may be between
about 1.4 and about 1.5
[0090] A porous layer (e.g., a porous intermediate layer) may be
made from materials including, but not limited to, silicon oxide,
anodic aluminum oxide (AAO), organo-silanes, organo-silicas,
organosilicates, organic polymers, inorganic polymers, and the
like, or any combination thereof. In some embodiments, a porous
layer may include low-k, porous low-k, or ultra-low-k dielectric
film. Low-k dielectric films used in the semiconductor industry,
i.e. organosilicate glass (OSG) films deposited by CVD of
organosilanes or by spin-coating of silsesquioxanes, may contain
sufficient porosity to enhance gas diffusion and decrease filling
time, however their mechanical properties (elastic modulus, E<10
GPa; hardness, H<2 GPa) are poorer than fused silica. Porous
layers including organic or inorganic polymers are also have much
lower mechanical properties compared to fused silica. Anodic
aluminum oxide (AAO) films have higher Young's modulus (.about.140
GPa) than fused silica with high porosity, but also have a higher
refractive index compared to fused silica (.about.1.7 vs. 1.46),
thus in this regard AAO may be less desirable as a porous layer
when capped with a silicon oxide film when optical pattern
inspection is considered.
[0091] A base layer and an intermediate layer or a cap layer may be
formed of the same or different materials. In some cases, a cap
layer may be more porous than base layer (e.g., to allow gases to
diffuse through the cap layer and into an intermediate layer). In
some cases, a cap layer may be less porous than intermediate layer
(e.g., to facilitate successful etching of the cap layer to form a
desirable patterned surface). In some embodiments, the cap layer is
more porous than the base layer and less porous than the
intermediate layer. A cap layer may be formed by material selected
to achieve desirable wetting and release performance during an
imprint lithography process.
[0092] In some embodiments, a cap layer may include a film of
porous SiO.sub.x with 1.ltoreq..times..ltoreq.2.5. For example, as
used herein, "porous SiO.sub.x" refers to silicon oxide that is
more porous than fused silica, less dense than fused silica, or
both. A thickness and composition of the cap layer may be chosen to
provide mechanical strength and selected surface properties, as
well as permeability to gases that may be trapped between a
substrate and a template in an imprint lithography process.
[0093] A thickness of an intermediate layer may be, for example, in
a range of about 10 nm to about 100 .mu.m, or in a range of about
100 nm to about 10 .mu.m. A thickness of an intermediate layer may
be increased to increase the capacity of the layer to accommodate
diffusion of gases into the layer. In some cases, a thicker
intermediate layer may provide higher effective permeability
without significantly reducing UV transparency, thermal expansion,
and the like.
[0094] A thickness of a cap layer may be in a range of about 10 nm
to about 10,000 nm (e.g., in a range of about 10 nm to about 50 nm,
about 50 nm to about 100 nm, about 100 nm to about 500 nm, about
500 nm to about 1000 nm, or about 1000 nm to about 10,000 nm).
Diffusion of gas through a cap layer is related to the porosity of
the cap layer as well as the thickness of the cap layer. In some
cases, a thickness of a cap layer may be selected based at least in
part on the porosity of the cap layer. That is, a more porous cap
layer may be thicker (e.g., about 5000 nm) than a less porous cap
layer (e.g., about 10 nm), such that gas can diffuse relatively
quickly through porous cap layers of various porosities and
thicknesses. If a cap layer is more porous than the layer to which
it is adhered, a thickness of a cap layer may be increased to
increase the capacity of the layer to accommodate diffusion of
gases into the layer. If the cap layer is adhered to a more porous
film, then it may be desirable to decrease the thickness of the cap
layer between the bottom of an etched feature and the more porous
layer to decrease diffusion resistance.
[0095] An intermediate layer may be formed by vapor deposition,
solution-based methods, thermal growth methods, or the like on a
base layer or on another intermediate layer. A cap layer may be
formed by vapor deposition, solution-based methods, thermal growth
methods, or the like on an intermediate layer or a base layer. As
used herein, "vapor deposition" generally refers to a process in
which a layer is formed from a vaporized precursor composition on a
surface of a substrate. Vapor deposition processes include, but are
not limited to, chemical vapor deposition (CVD), atomic layer
deposition (ALD), and physical vapor deposition (PVD). CVD
processes include, for example, plasma-enhanced CVD (PECVD),
low-pressure CVD (LPCVD), sub-atmospheric CVD (SACVD), atmospheric
pressure CVD (APCVD), high density plasma CVD (HDPCVD), remote
plasma CVD (RPCVD), and the like. PVD processes include
ion-assisted e-beam methods, and the like.
[0096] By varying the process conditions and materials, porous
layers with different mean pore sizes and pore size distributions
(e.g., different porosity or relative porosity) may be produced. An
intermediate layer and/or a cap layer may have pores with a larger
pore size and a greater porosity than fused silica. As used herein,
"porosity" refers to the fraction, as a percent of total volume,
occupied by channels and open spaces in a solid. The porosity of an
intermediate layer may range from about 0.1% to about 60% (e.g.,
about 1% to about 20%, or about 5% to about 15%). In some cases,
the porosity of an intermediate layer may be at least about 10%, or
at least about 20%. The porosity of a cap layer may range from
about 0.1% to about 20% (e.g., from about 1% to about 20%, or from
about 3% to about 15%).
[0097] Depositing SiO.sub.x by a vapor deposition process (e.g.,
PECVD) can yield a film with higher porosity than other processes
such as thermal oxidation or flame hydrolysis deposition. Vapor
deposition conditions that can be varied include temperature,
pressure, gas flow rates (e.g., for the silicon-containing gas, the
oxidation gas, the carrier gas, etc., or ratios thereof), electrode
distance, RF power, and bias.
[0098] In an example, oxide deposition from silane-PECVD can occur
according to the reaction shown below:
SiH.sub.4(g)+2N.sub.2O.sub.(g).fwdarw.SiO.sub.2(s)+2N.sub.2(g)+2H.sub.2(-
g).
Organosilicon materials such as tetraethyl orthosilicate (TEOS),
tetramethylsilane (TMS), and hexamethyldisilazane (HMDS) may also
be used with PECVD to form SiO.sub.x films.
[0099] The density of PECVD SiO.sub.2 has been shown by Levy et al.
("A comparative study of plasma enhanced chemically vapor deposited
Si--O--H and Si--N--C--H films using the environmentally benign
precursor diethyl silane," Mater. Lett. 54 (2002): 102-107, which
is incorporated herein by reference), to vary from 1.5 g/cm.sup.3
to 2.2 g/cm.sup.3 at deposition temperatures between 100.degree. C.
and 350.degree. C. The Young's modulus increased from 25 GPa to
over 70 GPa over this temperature range. PECVD has been reported to
generate silicon oxide films with a Young's modulus as high as 144
GPa at deposition temperatures of 250.degree. C. to 350.degree. C.
(Bhushan et al., "Friction and wear studies of silicon in sliding
contact with thin-film magnetic rigid disks," J. Mater. Res. 9
(1993) 1611-1628; and Li et al., "Mechanical characterization of
micro/nanoscale structures for MEMS/NEMS applications using
nanoindentation techniques," Ultramicroscopy 97 (2003) 481-494,
both of which are incorporated by reference herein).
[0100] A Young's modulus of 25 GPa is substantially higher than the
Young's modulus of films obtained from porous semi-conductor low-k
films, including organosilicate glass films deposited by CVD of
organosilanes or by spin-coating of silsesquioxanes. The hardness
of a PECVD SiO.sub.x film deposited at temperatures greater than
about 150.degree. C. may also exceed the hardness of a
semi-conductor low-k film. A PECVD SiO.sub.x film deposited at
about 350.degree. C. may have about 5% microporosity, as described
by Devine et al. ("On the structure of low-temperature PECVD
silicon dioxide films," J. Electron. Mater. 19(1990) 1299-1301,
which is incorporated by reference herein).
[0101] SiO.sub.x deposited on a fused silica substrate by PECVD
displays compressive stress believed to originate at least in part
from a mismatch of coefficients of thermal expansion. This mismatch
may be reduced by thermal annealing at moderate temperatures (e.g.,
a 500.degree. C. thermal cycle), as described by Cao et al.
("Density change and viscous flow during structural relaxation of
plasma-enhanced chemical-vapor-deposited silicon oxide films," J.
Appl. Phys. 96(2004) 4273-4280, which is incorporated herein by
reference). With selected annealing conditions, the nature of the
stress may become more tensile in nature, while still maintaining a
compressive to neutral stress desirable for a porous layer in an
imprint lithography template. As shown by Cao et al., the
coefficient of thermal expansion of a 10 .mu.m thick PECVD
SiO.sub.x film after a 500.degree. C. thermal cycle (about 0.55
ppm/.degree. C.) is similar to that of fused silica.
[0102] In some cases, annealing of a PECVD SiO.sub.x template layer
may promote densification of the SiO.sub.x film, resulting in lower
permeability. However, an annealing process carried out at lower
temperatures (e.g., about 100.degree. C. to about 350.degree. C.)
under controlled conditions (e.g., heating and cooling rates) may
maintain the porosity of the film.
[0103] Low temperature annealing experiments were carried out to
evaluate the impact of annealing on film stress. As shown in Table
4, a PECVD SIO.sub.x film (thickness of 5 .mu.m) on fused silica
had a calculated stress of -94 MPa after deposition. Following a
first 140.degree. C. annealing cycle, the stress was calculated as
-57 MPa. Following a second 140.degree. C. annealing cycle, the
stress was calculated as -42 MPa. The stress was calculated by the
Stoney equation. Radii were determined by measurements with a laser
interferometer (Mark GPI xps, available from Zygo Corporation,
Middlefield, Conn.), and film thickness was measured with a
spectroscopic reflectometer (available from Metrosol, Austin,
Tex.).
TABLE-US-00004 TABLE 4 Calculated stress of PECVD SiO.sub.2 film on
fused silica. Sample Calculated Stress As deposited 5 .mu.m PECVD
SiO.sub.2 film -94 MPa After first 140.degree. C. annealing cycle
-57 MPa After second 140.degree. C. annealing cycle -42 MPa
[0104] In some cases, forming a cap layer (e.g., a SiO.sub.x cap
layer) with a vapor deposition process on an intermediate layer may
clog pores in the intermediate layer. To reduce clogging of pores
in the intermediate layer, the intermediate layer may be
pre-saturated with inert gas. An exemplary PECVD process to reduce
clogging of pores in a porous substrate is shown in the flow chart
in FIG. 9. In process 90, after pumping the chamber (step 91),
purging the chamber (step 92), and pumping the chamber again (step
93), one or more inert gases are used to pre-saturate the chamber
and the porous substrate (step 94). The flow of inert gases is
stopped, and the CVD gases are introduced to the chamber and the
plasma is started (step 95).
[0105] In process 90, the CVD layer is thought to grow from the
surface of the intermediate layer for several reasons. For example,
since the pores have been saturated by inert gases, it is difficult
for CVD gases to diffuse into the intermediate layer. Additionally,
even though some of the CVD gases may get into the porous
intermediate layer, they are diluted with the inert gases inside
the intermediate layer and may not be present in sufficient
quantity to form a dense structure capable of blocking the pores
after reaction. Furthermore, since the plasma starts at
substantially the same time as the CVD gases are introduced into
the chamber, the reaction starts right away, and the CVD gases have
limited time to diffuse into the intermediate layer.
[0106] FIG. 10 illustrates a process of capping a porous first
layer 64 (e.g., an intermediate layer) with a thin layer of vapor
deposited SiO, as a second layer 63 (e.g., a cap layer) according
to the steps in FIG. 9. This process could also be applied in the
sealing of a cap, or the sealing of an asymmetric porous layer. As
shown in FIG. 10, porous first layer 64 is saturated with inert gas
65. Gas 69 (including silicon-containing gas, oxidation gas,
carrier gas, etc.) is introduced in a CVD process to form silica
second layer 63 on porous first layer 64. After second layer 63 is
formed on the surface of porous first layer 64, the porous first
layer will be effectively sealed, such that diffusion of the vapor
deposited gases, polymerizable material, and the like, into the
porous first layer is reduced or eliminated.
[0107] The gases used for pre-saturation may be inert toward
selected vapor deposition processes or may not react inside the
porous layer to clog the pores. The inert gas may be helium, neon,
argon, or nitrogen, or the like. In some cases, the vapor
deposition gas may be used as the inert gas. For example, in a
PECVD SiO.sub.x deposition process with SiH.sub.4 and N.sub.2O,
N.sub.2O may be used to pre-saturate a porous layer. Smaller
molecule gases such as helium and neon may diffuse out after the
process if their kinetic diameters are smaller than the pore size
of the seal layer. Larger molecule gases such as argon and nitrogen
might be trapped inside the a porous layer if their kinetic
diameters are larger than the pore size of the seal layer. Gases
trapped inside the porous layer may cause complications in future
applications. Therefore, smaller molecule gases may be
preferred.
[0108] Pre-saturation 91 in process 90 may range from about 5
seconds to about 60 min. The inert gas pressure may be at least the
same as the total vapor deposition gas pressure used for the vapor
deposition process and in some cases higher than the total vapor
deposition gas pressure. An initial deposition rate might be
slightly slower due to the dilution effect by the inert gases. To
achieve more precise vapor deposition layer thickness control, the
deposition rate may be re-calibrated between procedures. Different
inert gases may result in different initial deposition rates. The
deposition rate may to be re-calibrated when changing to a
different inert gas. Different inert gas pressure may also result
in a different initial deposition rate. The deposition rate may be
re-calibrated when changing to a different pre-saturation
pressure.
[0109] In certain circumstances, a porous layer may be subject to
internal tensile stress that leads to cracking or delaminating of
the film. As illustrated in FIG. 11, porous layer 68 may be subject
to intrinsic forces that produce a tensile force F.sub.T (or
compressive force F.sub.C) affecting the porous layer. For example,
tensile force F.sub.T (or compressive force F.sub.C) may result in
separation of porous layer 68 from base layer 62, angular
deformation, and the like.
[0110] The stress in a porous layer or film at ambient conditions
(e.g., room temperature, atmospheric pressure) may be tensile to
compressive (e.g., about +1 GPa to about -3 GPa, respectively). The
stress of a vapor deposited porous layer may be managed by a number
of methods, such as control of deposition conditions, annealing, or
stress relief films or layers.
[0111] Template 18 may include one or more relief layers 66
designed to mitigate the effects (e.g., template curvature) of
tensile force F.sub.T acting on porous layer 68. For example,
relief layer 66 may be designed having materials formed in a
compressive state such that compressive force F.sub.C acts on
relief layer 66. For example, relief layer 66 may be designed from
materials providing a set intrinsic stress level resulting in
compressive force F.sub.C. As such, compressive force F.sub.C
acting on relief layer 66 substantially neutralizes the tensile
force F.sub.T acting on porous layer 68 within template 18. In some
embodiments, one or more relief layers 66 may be designed to
mitigate the effects of compressive force F.sub.C (not shown)
acting on porous layer 68.
[0112] For example, FIG. 12 illustrates an exemplary embodiment of
template 18 having porous layer 68 adjacent to relief layer 66.
Relief layer 66 may be formed of materials providing a compressive
force F.sub.C such that compressive force F.sub.C substantially
reduces the effects of tensile force F.sub.T acting on porous layer
68. Relief layer 66 may be positioned on, substrate layer 62 using
techniques such as spin-coating, dip coating, CVD, PVD, thin film
deposition, thick film deposition, or the like, or any combination
thereof. The relief layer 66 may be formed of material including,
but not limited to SiNx, SiOxNy, SiCx, SiO.sub.x, DLC, and the
like, or any combination thereof. In some cases, relief layer 66
may be substantially transparent to UV light or wavelengths of
light used during the imprint process. Relief layers 66 may be
permeable to gases such as helium, nitrogen, oxygen, carbon
dioxide, and the like. In some embodiments, one or more relief
layers 66 may be designed to provide a tensile force F.sub.T such
that tensile force F.sub.T substantially reduces the effects of
compressive force F.sub.C (not shown) acting on porous layer
68.
[0113] FIG. 13A illustrates an exemplary embodiment of template 18
having multiple relief layers 66a and 66b adjacent porous layer 68.
Porous layer 68 may be permeable to gases such as helium, nitrogen,
oxygen, carbon dioxide, and the like. Relief layers 66a and 66b may
be formed of materials providing compressive forces F.sub.C1 and
F.sub.C2. Compressive forces F.sub.C1 and F.sub.C2 may be similar
or different in magnitude, depending on design considerations. For
example, compressive force F.sub.C2 of relief layer 66b may reduce
the effects of tensile force F.sub.T on porous layer 68 (e.g., may
reduce bending of the layer).
[0114] Relief layers 66a and 66b may be positioned on substrate
layer 62 and porous layer 68, respectively, using techniques such
as spin-coating, dip coating, chemical vapor deposition (CVD),
physical vapor deposition (PVD), thin film deposition, thick film
deposition, or the like, or any combination thereof. Relief layers
66a and 66b may use similar positioning methods or different
positioning methods depending on design considerations.
[0115] Additionally, relief layers 66a and 66b may be formed of
similar materials or different materials depending on design
considerations. For example, as relief layer 66a may be positioned
within the diffusion path of gases 60 (not shown), relief layer
66a, having a thickness t.sub.R1, may be formed of materials
permeable to gases 60 present during the imprint process.
Alternatively, relief layer 66b may have a thickness t.sub.R2 that
is greater than thickness t.sub.R1 and may be formed of less
permeable materials as the majority of stress compensation may
occur at relief layer 66b. Additionally, relief layer 66b may be
formed of permeable material to facilitate diffusion of gases into
substrate layer 62, depending on design considerations. In some
embodiments, as illustrated in FIG. 13B, relief layer 66a may be a
patterned relief layer 66a having features 24 and 26 formed
therein. In some embodiments, relief layers 66a and 66b may be
formed of materials providing tensile forces F.sub.T1 and F.sub.T2
to reduce the effects of compressive force F.sub.C (not shown) on
porous layer 68.
[0116] FIG. 14 illustrates an exemplary embodiment of template 18
having multiple relief layers 66 to relieve tensile stress within
multiple porous layers 68. In particular, template 18 comprises
relief layers 66c-e that may be interspersed between permeable
layers 68a and 68b such that compressive forces F.sub.C1-C3 reduce
the effect of (e.g., the bending moments caused by) tensile forces
F.sub.T1-T2. Relief layers 66c-e may use similar positioning
methods or different positioning methods depending on design
considerations. Additionally, relief layers 66c-e may be formed of
similar materials and have similar physical characteristics (e.g.,
thickness) and/or different materials and physical characteristics
depending on design considerations. An analogous embodiment may
provide relieve of compressive stress F.sub.C1-C3 caused by tensile
forces F.sub.T1-T2 (not shown).
[0117] Referring to FIG. 15A, template 110 shows stress indicated
as bending of layer or film 112 on the imprinting surface of the
template. Referring to FIG. 15B, stress relief layer 114 is formed
on the surface of template 110 opposite layer 112. Stress relief
layer 114 relieves the stress in layer 112 by providing a bending
moment which reduces the curvature of the layer. In some
embodiments, stress relief layer 114 may provide compressive stress
to reduce compressive stress of layer 112. In some embodiments,
stress relief layer 114 may provide tensile stress to reduce
tensile stress or to impart a compressive stress to layer 112.
Etch Stop layer
[0118] Referring to FIG. 16, template 100 includes a base layer
102, an etch stop layer 104, and a top layer 106. Etch stop layer
104 and top layer 106 differ with respect to certain physical
properties (e.g., index of refraction), such that interface 108
between the etch stop layer and the top layer can be used as a
reference point during nano-imprint lithography fabrication
processes that include etching or chemical mechanical planarization
(CMP) of the top layer. Etch stop layer 104 and top layer 106 also
differ with respect to certain chemical properties (e.g.,
reactivity with known etching processes).
[0119] Template 100 may be, for example, bulk fused silica. Etch
stop layer 104 may be substantially UV transparent and have low UV
absorbance. In an example, etch stop layer 104 may include a metal,
a metal oxide, or a metal nitride. In some cases, etch stop layer
104 consists essentially of Si.sub.xN.sub.y. Top layer 106 may be
porous (e.g., porous silica). In some cases, top layer 106 includes
SiO.sub.x, with 1.ltoreq..times..ltoreq.2.5.
[0120] The different physical characteristics of the etch stop
layer 104 and the top layer 106 (e.g., different indices of
refraction) allow optical/metrological assessment of the thickness
of the top layer, as measured with respect to the interface 108
between etch stop layer 104 and top layer 106. Because a depth of
top layer 106 can be accurately and precisely measured with respect
to etch stop layer 104, top layer 106 can be polished back (e.g.
with chemical mechanical planarization) to a known measurable
distance from the etch stop layer 104 to enable etching processes
in nano-imprint lithography template fabrication used to pattern
top layers with known and reproducible dimensions (e.g., residual
layer thickness, protrusion height, aspect ratio, and the
like).
[0121] Etching processes that etch top layer 106 but not etch stop
layer 104 may include any etching process that is known to etch
silica (e.g., reactive ion etching). Thus, the different chemical
properties of the etch stop layer 104 and the top layer 106 allow
etching of the top layer without etching of the etch stop layer.
The presence of etch stop layer 104 allows the top layer 106 to be
completely removed by etching while leaving the etch stop layer and
the base layer substantially unaltered. Thus, top layer 106 can be
removed, changed, or replaced, as desired. The ability to reuse the
base layer of the template is economically advantageous, and allows
conservation of resources.
Metrology Marker
[0122] In some cases, a region of a base layer or intermediate
layer of an imprint lithography tem 100 plate may be coated with a
marker film. FIG. 17A illustrates an imprint lithography template
100 with base layer 102, top layer 106, and marker region 107
formed at an interface between the base layer and the top layer.
Marker region 107 may cover a small portion of the base layer 102
(e.g., less than about 1 cm.sup.2). A thickness of marker region
107 may be between about 2 nm and about 30 nm, such that a flatness
of the upper surface of the top layer is substantially unaffected
by the presence of the marker region. In some cases, top layer 106
may be polished smooth and flat (e.g., with chemical mechanical
planarization) before patterning and etching features on the
template. A thickness of marker region 107 may be used as a
reference to determine a depth of etching of top layer 106. The
material used to form marker regions 107 may include, for example,
a metal, a metal oxide, or a metal nitride.
[0123] One or more marker regions 107 may be spaced apart from an
active (e.g., patterned) portion of the top layer 106. Placing a
metrology marker outside the mesa (e.g., placing four markers
outside the corners of the mesa) would allow UV radiation to pass
through the template and into the polymerizable fluid without
blocking, and would reduce the total amount of radiation absorbed
(and thus the amount of heating of the template) compared to a
continuous stop etch layer.
[0124] In some cases, rather than depositing a small marker region,
one or more areas of a template may be masked during coating of a
base layer or coating of an intermediate layer with another layer
(e.g., a porous layer). A difference in height between the masked
area 109 and the coated portion 111 may serve as a reference for
coating depth, etching depth, or polishing depth.
[0125] FIG. 17B illustrates a nano-imprint lithography template
with marker regions 107 deposited on base layer 102. Porous layer
103 is formed over base layer 102 and marker regions 107. Porous
layer 103 may be polished before seal layer 105 is deposited on the
porous layer. The seal layer may inhibit dogging of the porous
layer during formation of cap layer 106. That is, during formation
of cap layer 106, the presence of the seal layer may inhibit
infiltration and thus clogging of the porous layer with components
(e.g., reactive species) used to form the cap layer. In some cases,
based on the properties of porous layer 103 and the cap layer 106,
the seal layer 105 may be omitted.
Chemical Mechanical Planarization
[0126] In embodiments discussed herein, a layer of a template
(e.g., a cap layer, an intermediate layer) may undergo chemical
mechanical planarization (CMP). CMP includes the polishing of one
or both sides of a substrate simultaneously, using both chemical
and mechanical means. An imprint lithography template is held in a
carrier housing. Slurry is dispensed on a polishing pad. The
template is rotated and oscillated (eccentric motion) and is
brought into contact with a rotating polishing pad. The force of
the substrate against the pad is controlled. The slurry both reacts
with the surface (chemical aspect of CMP) and physically scrubs the
surface (mechanical aspect of CMP). The abraded material is carried
away by the polishing pad.
[0127] Surfaces formed by some PECVD processes, such as silicon
oxide film deposition, may be undesirably rough. The roughness
reduces the usefulness and desirability of these surfaces for use
as an imprint surface for patterning, or for use as a base layer
for the deposition of a conformal film. CMP can be used to polish a
rough layer to substantially eliminate the roughness and improve
flatness and parallelism of the template. CMP may also improve
filling speed by reducing a roughness of a layer that contacts the
imprint resist.
EXAMPLES
Example 1
[0128] The enhanced diffusion performance of low-temperature PECVD
SiO.sub.x was shown through imprint testing. Samples for imprint
filling tests were generated by depositing porous silicon oxide by
PECVD (PlasmaTherm 790 RIE/PECVD) at 200.degree. C. to a thickness
of 5 .mu.m on double-side polished (DSP) 3'' silicon wafers having
a nominal thickness of 375 .mu.m. The Si source was SiH.sub.4, with
a flow rate of 21.2 sccm. The oxidizing agent was N.sub.2O, with a
flow rate of 42 sccm. The deposition total pressure was 300 mTorr,
and the RF power was 50 W. The wafer was placed directly on the
chuck for deposition. The wafers were then spin-coated with 60 nm
of TranSpin.TM. (available from Molecular Imprints, Inc., Austin,
Tex.). As a control, a 3'' DSP silicon wafer was coated with 60 nm
of TranSpin.TM.. A 65 mm fused silica core-out template was used to
generate imprints with a residual layer thickness of about 90 nm
using a grid drop pattern with a 340 .mu.m drop center-to-center
distance. Helium was used as the purge gas.
Example 2
[0129] FIGS. 18A and 18B show images of drops of imprint resist 180
in a helium environment taken through a template including a 5
.mu.m porous silicon oxide cap layer formed on the wafer by PECVD.
As shown in FIG. 18A, drop interstitial regions 182 were observed
by a microscope camera at the time the template contacted the
resist. The image in FIG. 18B was taken 1 second after the template
contacted the resist. Within 1 second after the resist was
contacted by the template, gas pockets in the interstitial
locations 182 disappeared, and imprint resist 180 spread to
substantially cover the template.
[0130] FIGS. 19A-19C show images of drops of imprint resist 180 in
a helium environment taken through a template similar to that in
FIG. 18A, without the 5 .mu.m porous silicon oxide cap layer. FIG.
19A shows drops of imprint resist 180 and interstitial regions 182
as observed by a microscope camera at the time the template
contacted the resist. FIGS. 19B and 19C show interstitial regions
182 still present 1 second later and 4 seconds later, respectively.
Thus, the porous oxide layer allowed for the quick uptake of
helium, which resulted in the void filling more than 4 times faster
than the same void on an imprint made on a silicon wafer without
the porous silicon oxide layer.
Example 3
[0131] Table 5 lists PECVD process conditions for the formation of
four silicon oxide layers and a thermal oxide layer. Films were
grown on DSP 3'' silicon wafers to 1.5 .mu.m thickness in a
PlasmaTherm 790. Due to the fixed-position chuck of the PlasmaTherm
790, the silicon wafers were placed on top of a 3.5''
diameter.times.0.25'' polished fused silica plate instead of
directly on the chuck in order to better approximate the growth
conditions for a 0.25'' thick fused silica template. Indentation
hardness and modulus of the PECVD silicon oxide films were measured
on a CSM Instruments NHTX nanoindentation tester with an indentor
of Berkovich geometry. PECVD silicon oxide film density was
measured by X-ray spectroscopy (XRR).
TABLE-US-00005 TABLE 5 Example PECVD Process Conditions.
Indentation Indentation N.sub.2O SiH.sub.4 Power Pressure Temp
Density Modulus Hardness Sample (sccm) (sccm) (W) (mTorr) (.degree.
C.) (g/cc) (GPa) (GPa) 1 42 21.2 50 300 270 1.83 49.6 4.8 2 42 21.2
50 300 300 1.96 Not Not measured measured 3 42 21.2 100 1000 335
2.11 Not Not measured measured 4 42 21.2 50 300 335 Not 53.1 5.0
measured Fused silica 2.20 E = 72.4.sup.a Hv = 7.7 GPa
.sup.aTechnical Data Sheet, Shin-Etsu Synthetic Quartz, Shin-Etsu
Chemical Co., Ltd.
[0132] Fused silica is provided for comparison. The density was
measured by XRR. Sample 1 is 83% as dense as the non-porous fused
silica, Sample 2 is 89% as dense, and Sample 3 is 96% as dense.
Even with a 17% change in relative porosity for the most porous
sample, the modulus of Sample 1 was 49.6 GPa and the hardness was
4.8 GPa. Sample 1 has a ratio of Young's modulus to relative
density of (49.6/0.83)=59.8, and a refractive index of 1.47.
Example 3
[0133] A test was developed to provide a comparison of open
porosity for different films by dispensing drops of imprint resist
on a PECVD silicon oxide surface and observing the drop diameter by
optical microscope over time to determine if the resist was
penetrating the film. The films listed in Table 6 were deposited on
DSP 3'' wafers while the wafers were spaced apart from the chuck by
a 1/4'' thick polished fused silica plate. Drops that maintained
approximately the same diameter for 2 minutes (a slight change can
occur due to evaporation) were considered "non-wicking." Various
wicking rates were observed as indicated in Table 6. The wicking
rates were seen to vary depending on the deposition conditions as
listed in Table 6. The filling rates were obtained from 90 nm thick
imprints obtained by depositing droplets spaced 340 .mu.m apart on
a rectangular grid in a helium-purged environment. After wicking
but before the filling test, the silicon oxide coated wafers were
coated with TranSpin.TM. to (a) seal the open surface pores to
prevent resist from wicking in during imprinting and to (b) serve
as an adhesion promoter for the resist. Filling times are expected
to decrease for highly-polished films as an imprinting surface in
comparison to films with rough surfaces. The refractive indices of
the films were measured on a J.A. Woollam M-2000 DI
ellipsometer.
TABLE-US-00006 TABLE 6 Example PECVD process conditions. Filling
Film Refractive Film N.sub.2O SiH.sub.4 Power Pressure Temp Time
time Thickness index at Stack Layer (sccm) (sccm) (W) (mTorr)
(.degree. C.) (min) Wicking (sec) (um) .lamda. = 600 nm A Single
160 7.0 80 800 335 40 none Not Not 1.4639 tested measured B Single
42 21.2 50 450 335 90 none 2.4 4.9 1.4585 C Single 42 21.2 50 300
270 80 fast 1.2 4.1 1.4717 D Intermed. 42 21.2 50 300 270 80 none
Not 4.4 Not meas. Cap 160 7.0 80 800 270 18 tested 0.4 E Single 42
21.2 50 1000 335 130 none 1.8 Not 1.4603 measured F Single 120 21.2
100 300 335 80 none Not Not 1.4487 tested measured G Single 42 21.2
50 1000 335 65 None 2.1 4.3 1.4488
[0134] Film C is porous and is intended to be coated with a cap
layer for further processing (e.g., sealing, patterning, and
feature etch). This film is an example of a layer that is suitable
as a porous first layer (e.g., a porous intermediate layer). The
porosity is apparent by the measured density, drop wicking result,
and fast filling time compared to the denser single layers listed
in Table 6.
[0135] Film D includes a cap on Film C. A lower temperature cap
process (270.degree. C.) was used which was the same temperature as
the first layer. This lower temperature process may reduce unwanted
thermal changes in the first (intermediate) layer during the second
layer deposition, because the temperature does not exceed above the
first layer process.
[0136] Films B, E, F, and G were processed at 335.degree. C. and
all demonstrate non-wicking attributes. Other process conditions
(e.g., gas flow rate, pressure, and power) were varied as noted in
Table 6. A denser cap is preferred for patterning of features into
a film. Furthermore, films E and G are formed by the same process,
but film E is twice as thick (about 8 .mu.m) as Film G (about 4
.mu.m). Film thicknesses were obtained by cross-sectioning and
measuring by SEM.
[0137] FIGS. 20A and 20B show photographs of wicking of an imprint
resist on Film C. The image in FIG. 20A was taken once the wafer
stage was settled after the imprint resist was deposited as drops
of imprint resist 180 on Film C. The drops of imprint resist 180
penetrate the film quickly. The outlines of the drops are no longer
distinguishable in FIG. 20B, taken 5 seconds after the image in
FIG. 20A. The drops 180 spread quickly as the gases between the
drops diffused through the film
[0138] FIGS. 21A and 21B show images of spreading of an imprint
resist on Film D. The image in FIG. 21A was taken once the wafer
stage was settled after the drops 180 were dispensed onto the film.
FIG. 21B, taken 120 seconds later, shows substantially no change in
the size of drops 180. Film D is considered to be an example of a
non-wicking film.
Example 4
[0139] A fused silica template measuring 65.times.65.times.6.4 mm
was fabricated with a PECVD porous silicon oxide film to
demonstrate enhanced gas diffusion through the template side versus
the wafer side. A layer of silicon oxide about 4 .mu.m thick was
grown on the surface of a cored-out fused silica template having a
mesa measuring 26.times.32 mm and 15 .mu.m in height. The cored-out
region of the template was set on a 2'' diameter.times.0.25'' thick
polished fused silica plate that was placed on the chuck in a
PlasmaTherm 790. After deposition of a porous silicon oxide layer,
an organic polymer and a silicon-containing polymer were spin
coated on top of the porous silicon oxide, film to planarize the
topography and cap the porous film to prevent imprint resist from
penetrating into the oxide. Spin coater CEE.RTM. 4000, available
from, Brewer Science (Rolla, Mo.), was used in the spin coating
process. The template was spin coated with 100 nm of TranSpin.TM.
and proximity baked on a hotplate with the coated side facing down
at 160.degree. C. for 3 min. The template was then spin coated with
100 nm of a high-silicon containing polymer resist similar to the
class of materials described in U.S. Pat. No. 7,122,079, which is
incorporated herein by reference, and proximity baked on a hotplate
with the coated side facing down at 160.degree. C. for 3 min.
Because a mesa was on the template prior to spin coating, an edge
bead formed along the sides of the top surface of the mesa,
therefore a diced silicon wafer piece measuring approximately
20.times.20 mm was used as a mask during a dry-etch process to
remove the edge bead and to define a new mesa in the silicon oxide
layer. The silicon mask was then removed and the template was
exposed to low power oxygen plasma to oxidize the surface of the
high-silicon containing polymer to impart some SiOx character for
wetting and release properties. The template was etched and
oxidized in a Oracle III etcher available from Trion Technology
(Clearwater, Fla.).
[0140] The template was imprinted in a helium purged environment on
200 mm DSP silicon wafers coated with 60 nm of TranSpin.TM..
MonoMat.RTM. imprint resist, available from Molecular Imprints,
Inc., was dispensed in a rectilinear grid pattern having an
approximate drop spacing of 340 .mu.m center-to-center to produce
imprints about 90 nm thick. As shown in FIG. 22A, interstitial
locations 182 between drops of imprint resist 180 were observed by
a microscope camera at the time the template contacted the resist.
Images in FIGS. 22B, 22C, and 22D were taken 0.3 sec, 0.7 sec, and
1.2 sec, respectively, after the image in FIG. 22A. As seen in FIG.
22D, the interstitial locations 182 disappeared within 1.2 seconds
after the resist was contacted by the template, such that the
surface of the template was substantially covered with imprint
resist.
[0141] The photographs shown in. FIGS. 19A-19C were taken through a
fused silica template that did not contain a porous film, but was
imprinted on a similar film stack as above. FIG. 19C shows the
interstitial gas pocket remaining after 4 seconds. Thus, the porous
silicon oxide layer allowed for the quick uptake of helium, which
resulted in the void filling more than 3 times faster than a
similar void with a fused silica template which did not have a
porous oxide layer.
[0142] Further modifications and alternative embodiments of various
aspects will be apparent to those skilled in the art in view of
this description. Accordingly, this description is to be construed
as illustrative only. It is to be understood that the forms shown
and described herein are to be taken as examples of embodiments.
Elements and materials may be substituted for those illustrated and
described herein, parts and processes may be reversed, and certain
features may be utilized independently, all as would be apparent to
one skilled in the art after having the benefit of this
description. Changes may be made in the elements described herein
without departing from the spirit and scope as described in the
following claims.
* * * * *